Method for preparing an imidized polymer

1. Process for preparing an imidized polymer which comprises reacting in a mixing or kneading device a mixture, comprising (i) an olefin copolymer comprising from 15 to 80 wt % of ethylene, from 20 to 85 wt % of a C 3 -C 10 alpha-monoolefin, from 0 to 15 wt % of a polyene selected from non-conjugated dienes and trienes and from 0.1 to 10 anhydride groups or derivatives thereof per 1000 C-atoms, and (ii) an aromatic polyamine compound of which at least one of the amine groups is a primary amine, in the presence of between 1 and 4 mol % based on the amount of the polyamine of an acid.

2. Process according to claim 1 , wherein the aromatic polyamine compound is selected from:

(a) an N-arylphenylenediamine represented by the formula:

in which Ar is aromatic and R 1 is —H, —NH 2 , —(—NH-Aryl) n -H, —(—NH-Alkyl) n -H, —NH-arylalkyl, a branched or straight chain radical having from 4 to 24 carbon atoms that can be alkyl, alkenyl, alkoxyl, aralkyl, alkaryl, hydroxyalkyl or aminoalkyl, R 2 is

(—NH 2 , —(NH(CH 2 ) n —) m —NH 2 , —(CH 2 ) n —NH 2 , -aryl-NH 2 , in which n and m has a value from 1 to 10, and R 3 is hydrogen, alkyl, alkenyl, alkoxyl, aralkyl, alkaryl having from 4 to 24 carbon atoms, preferably is R 1 equal H, R 2 equal —NH2, and R 3 equal H, which is N-phenyl phenylene diamine (NPPDA) and its isomers,

(b) an aminocarbazole represented by the formula:

in which R and R 1 represent hydrogen or an alkyl, alkenyl, or alkoxyl radical having from 1 to 14 carbon atoms,

(c) an aminoindole represented by the formula:

in which R represents hydrogen or an alkyl radical having from 1 to 14 carbon atoms,

(d) an amino-indazolinone represented by the formula:

in which R is hydrogen or an alkyl radical having from 1 to 14 carbon atoms,

(e) an aminomercaptotriazole represented by the formula:

in which R can be absent or can be C 1 -C 10 linear or branched hydrocarbon selected from the group consisting of alkyl, aryl, alkaryl, or arylalkyl,

(f) an aminopyrimidine represented by the formula:

in which R represents hydrogen or an alkyl or alkoxyl radical having from 1 to 14 carbon atoms.

3. Process according to claim 1 , wherein the acid has a pKa <4.

4. Process according to claim 3 , wherein the acid is PTSA or DBSA.

5. Process according to claim 4 , wherein the amount of PTSA is between 1 and 3 mol % based on the polyamine.

6. Process according to claim 1 , wherein the mixing device is a twin screw extruder.

7. Process according to claim 1 , wherein at least the last part of the reaction is carried out in a static mixer device or a kneading device.

8. Process according to claim 7 , wherein the reaction mixture is degassed after the static mixer device or kneading device by means of an in line single screw extruder.

9. Process according to claim 1 , wherein the molar ratio between the aromatic polyamine compound and the anhydride groups of the polymer is between 0.9 and 1.2.

10. Process according to claim 1 , wherein the temperature of the reaction mixture in the static mixer device is at least 275° C.

11. A solid multifunctional viscosity modifier comprising a polymer comprising between 0.1 and 10 functional groups per 1000 C-atoms, wherein the functional groups comprising aromatic amine-based imide groups, and wherein the imide and functional groups are present in a ratio of the imide groups to the functional groups of more than 0.85.

12. Lubricating oil composition, comprising the solid multifunctional viscosity modifier according to claim 11 , wherein the amount of low molecular weight aromatic polyamine comprising compound in the oil is smaller than 10 ppm.

13. The solid multifunctional viscosity modifier as in claim 11 , wherein the ratio of the imide groups to the functional groups is more than 0.90.

14. The solid multifunctional viscosity modifier as in claim 11 , wherein the ratio of the imide groups to the functional groups is more than 0.95.